Why high end glass is the best choice for your photobioreactor

If your main concerns are the algae production costs, the lifetime of the PBR system and the total cost of ownership, you are definitely making the right choice with a tubular glass PBR. However, even when choosing among glass PBRs, there are significant differences. These differences can have a profound impact on the final system performance and therefore it is crucial that you are aware of them.

Borosilicate glass – the best glass for a photobioreactor

The glass of the PBR tubes need to withstand numerous environmental impacts and cleaning processes, so that you can productively cultivate algae within them over many years. This is why SCHOTT uses borosilicate glass. This glass type is:

UV-stable: The glass’ light transmittance stays almost constant, even when being exposed to decades of solar radiation and UV radiation.

Chemically stable: Therefore, the glass tubes can be cleaned and disinfected with numerous chemical solutions to remove bio fouling within the reactor.

Salt resistant: This is especially important when planning on cultivating saltwater algae.

Find out more about the physical and chemical characteristics of borosilicate glass in our factsheet about borosilicate glass.

Why is high end glass better?

The right type of glass is not the only relevant aspect when choosing glass tubes for a PBR. Just as important is the way the glass is manufactured, how the glass tube is processed and how the system as a whole is designed. Therefore, high end glass components with high productivity and excellent cost benefit calculation differ from lower quality ones.

PBR tubes usually have a wall thickness between 2.5 and 3.3 mm. Tests have shown, that a thinner wall with an outside diameter of 65 mm can lead to up to 10% more profit. Therefore, SCHOTT offers tubes with an outside diameter of 65 mm and a wall thickness of 2.2 mm and tubes with an outside diameter of 54 mm and an even thinner wall thickness of 1.8 mm.

Single glass tube segments for photobioreactors that are available on the market are often only 2-4 meters long. The longer the tube is, the less segments that have to be connected for the total volume. This means, there are less tube transitions and less tube couplings needed. With every saved tube coupling, the costs decrease. Also due to the lower amount of tube transitions, the risk of biofilm formation within the couplings is also decreased. SCHOTT therefore offers 5.5 meter long tubes in their standard range.

In a photobiorector, numerous tube segments are usually connected to make one total tube. These tubes are built together in different levels with U-bends or manifolds to create the complete PBR system. Ideally, the tubes are of the same length. To be able to connect the tube couplings on each side with U-Bend or manifolds, it is essential, that the tube ends lie on one level. Only then, it is possible to couple them with the U-bend or manifold arms without any gaps. Otherwise, these gaps can lead to bio fouling. Additionally, tension can occur within the system. If the tube lengths are different, the worst case scenario is that it’s no longer possible to use professional tube couplings. Cutting tube glass to an exact length is a technical challenge. SCHOTT can produce 5.5 m long tubes with a length tolerance of +/- 2 mm.

A common misconception of glass: It apparently breaks very easily. This however, only applies to poorly produced glass tubes. SCHOTT has automated and standardized its production processes to a great extent. This allows us to secure, through slow and balanced cooling, no tension is frozen into the glass tube. These tensions are the reason why tubes can break under low mechanical impact. Additionally, the ends of the tube segments are melted once again. The objective of this measure is to prevent micro fissures at the tube ends. The sum of these aspects results in SCHOTT customers not having any problems with tube ruptures.

SCHOTT not only delivers glass tubes, but a coordinated system revolving around the glass components. Besides the tubes, SCHOTT also offers the suitable U-bends and manifolds. Furthermore, SCHOTT provides special couplings to ensure that all components can be connected in a fast, safe and reutilized manner.

The advantages of high end glass at a glance

With the application of high end glass within a photobioreactor you can implement the following advantages:

Long lifespan of your photobioreactor of up to 50 years due to mechanically tension free and stable glass

Higher productivity through thinner tube wall thickness

Easy, tension free construction of the PBRs without gaps due to the same tube lengths